Surface Spectroscopy of Room- Temperature Ionic Liquids at the Platinum-Liquid Electrochemical Interface

摘要

In situ vibrational spectroscopy using sum frequency generation, SFG, is performed to investigate room- temperature ionic liquids at the platinum electrode surface. The ionic liquid studied is 1-butyl-3-methylimidazolium tetrafluoroborate, BMIM-BF4. SFG spectra are collected as a function of applied potential.(Figure 1) Vibrations due to C-H of the butyl chain, and C-H of the imidazolium ring are identified.(Figure 2) The polarized SFG spectra are examined to estimate the orientation of the cation at the surface. The cation appears to be oriented with the ring tilted along the surface normal and the butyl chain extended parallel to the surface. Further, SFG spectra are conducted at the potential limits to determine the presence of degradation products of the electrochemical reaction. The influence of water (a common impurity) on this ionic liquid is also probed with SFG. Preliminary results on the anion influence between BF4- and PF6- on the cation orientation are shown. Results of the ionic liquid-solid interface are compared to the ionic liquid-gas interface.